1. Field of the Invention
This invention relates to the area of technology known generally as "composite materials", and in particular to methods and apparatus for producing composite materials and structures of increased strength.
2. Background Information
Composite materials consisting of fibers and a matrix of resin are used to produce a wide range of useful products, from fiberglass sail boats to the recent radar transparent, stealth aircraft. Structures of composite materials have numerous advantages that include the promise of higher strength and lower weight than those of other materials such as metal. The promise has not been fulfilled, however, because some composites materials, principally those using graphite fibers, have compressive strengths that are only a fraction of the tensile strength. Theoretically, composite materials of graphite fiber should have a compressive strength that equals the tensile strength. In practice the compressive strength is much less for reasons that have not been fully understood.
It has been demonstrated that composite materials that include curved graphite fibers have a reduced fatigue resistance. It has been suggested that waviness of graphite fibers in a composite material can reduce compressive strength.
Meanwhile, the commercially available composite materials that include graphite continue to be made with fibers that by reason of waviness, or some other reason, have decreased compressive strength. As a result, the promise of reducing weight by the use of composite materials has not been realized, with a consequent increase in cost and a decrease in performance in structures such as aircraft.